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Print a working paper computer on an $80 inkjet

Ink laced with silver nanoparticles could make it a reality, to the joy of hobbyists

By Paul Marks

Digital filigree

(Image: Sensprout)

“IMAGINE printing out a paper computer and tearing off a corner so someone else can use part of it.” So says Steve Hodges of Microsoft Research in Cambridge, UK. The idea sounds fantastical, but it could become an everyday event thanks in part to a technique he helped develop.

Hodges, along with Yoshihiro Kawahara and his team at the University of Tokyo, Japan, have found a way to print the fine, silvery lines of electronic circuit boards onto paper. What’s more, they can do it using ordinary inkjet printers, loaded with ink containing silver nanoparticles. Last month Kawahara demonstrated a paper-based moisture sensor at the Ubicomp conference in Zurich, Switzerland.

Kawahara says the idea is perfect for the growing maker movement of inventors and tinkerers. Hobbyists will be able to test circuit designs by simply printing them out and throwing away anything that doesn’t work. That will reduce much of electronics to a craft akin to “sewing or origami”, he says.

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Hobbyists can test circuits by simply printing them out, reducing electronics to a craft akin to sewing

Kawahara and Hodges say the idea also fills a gaping void in the capabilities of 3D printers, which can print the casing for a gadget but not the printed circuits that go inside it. Research on 3D printing conductive elements inside structures has not yet reached a level of sophistication for it to be useful.

“Designing a printed circuit board is not a trivial thing at all. So many people talk about 3D printing an iPhone, when all you can actually do is print a few limited components of one,” says Matt Johnson, founder of London firm Bare Conductive, which makes conductive ink for hobbyists. He says there need to be easier ways for people to create circuitry that could lend itself to novel applications such as packaging (see “Ink gets wired for sound“).

The ink used by Kawahara’s team is a silver suspension recently developed by Mitsubishi Chemical in Tokyo. Kawahara tried it out in an &dollar;80 inkjet printer and discovered that it worked well on photo-quality paper. The ink needs no heat to release its silver, and the particle size, viscosity and surface tension were just right for it to deposit flat silver conductors onto the paper. To turn these into working circuits, the team avoided soldering – which would have burned through the paper – and instead used a conducting glue to attach components like resistors and capacitors.

The moisture sensor the team has printed is meant for use on plants (see picture). It detects rainfall with one circuit and soil humidity with another, transmitting its readings via a printed Wi-Fi antenna. Hodges has printed paper wiring to connect the switch, LED and battery of a 3D-printed flashlight.

In addition, the team has shown off more complex inkjet-printed circuits, with microprocessors and memory chip connectors. In principle, these could be used to create paper-based computers that would continue to work even when broken into smaller pieces. Jürgen Steimle at the Massachusetts Institute of Technology is already developing “redundant” circuit layouts with this capability, including circuitry for touchpad-like devices that work even if one part has been cut out. It raises the prospect of printed devices that people could simply tear to share.

If silver-based inkjet printing can be made affordable, Hodges says it will be a natural follow-on to Bare Conductive’s hand-drawn and paintable circuitry. Kawahara goes further&colon; “In 20 years you really will be able to hit ‘Print’ and make yourself a mobile phone”.

Ink gets wired for sound

Bare Conductive is a London-based start-up that makes conductive ink (see main story). This allows touch-sensitive light switches to be painted on worktops, for example. The firm also makes greeting cards that children can draw on using pens filled with the ink, connecting up batteries to LEDs to make them flash.

Now the firm wants to add audio output to its cards – and future interactive packaging – using a circuit it calls a TouchBoard. The size of a playing card, it features a simple to use Arduino processor and an MP3 chip that plays music, stories and sound effects when someone taps the painted-on, conductive buttons. A Kickstarter campaign to build TouchBoard is about to be launched.

This article appeared in print under the headline “Tear me to share me”